Add the QOverload snippet to overloaded slots, not just to overloaded signals

For a while we've had in the docs a small autogenerated snippet that explains how to pick a signal in an overload set. E.g. for QComboBox::currentIndexChanged there's

https://doc.qt.io/qt-5/qcombobox-obsolete.html#currentIndexChanged-1

Now, of course we're trying to rename signals and slots as much as possible to avoid overloads, but we still have some. Could a similar snippet be added to overloaded slots?

https://doc.qt.io/qt-5/qlcdnumber.html#display-2